# std::layout_left::mapping

From cppreference.com
< cpp‎ | container‎ | mdspan‎ | layout left

Defined in header `<mdspan>` |  |
template< class Extents > class layout_left::mapping; |  | (since C++23)

The class template `layout_left::mapping` controls how multidimensional indices are mapped in a column-major manner to a one-dimensional value representing the offset. The mapping has stride 1 at leftmost extent and strides increase left-to-right as the products of extents.

Every specialization of `mapping` is a LayoutMapping and a TriviallyCopyable type which satisfies `regular`.

The program is ill-formed if the size of the multidimensional index space Extents() is not representable as a value of type Extents::index_type when Extents::rank_dynamic() is ​0​.

### Template parameters

Extents | - | specifies number of dimensions, their sizes, and which are known at compile time. Must be a specialization of `std::extents`.

### Member types

Member type | Definition
`extents_type` | `Extents`
`index_type` | `extents_type::index_type`
`size_type` | `extents_type::size_type`
`rank_type` | `extents_type::rank_type`
`layout_type` | std::layout_left

### Data members

Member | Definition
`extents_type` `extents_` (private) | the extents object (exposition-only member object*)

### Member functions

(constructor) | constructs a new mapping (public member function)
operator= (explicitly defaulted) | assigns a mapping (public member function)
##### Observers
extents | obtains the extents object (public member function)
required_span_size | returns the required size of the mapping (public member function)
operator() | maps a multidimensional index into an offset value (public member function)
is_unique [static] | determines if this mapping is unique (every combination of indices maps to a different underlying element) (public static member function)
is_exhaustive [static] | determines if this mapping is exhaustive (every underlying element can be accessed with some combination of indices) (public static member function)
is_strided [static] | determines if this mapping is strided (in each dimension, incrementing an index jumps over the same number of underlying elements every time) (public static member function)
is_always_unique [static] | determines if this layout mapping is always unique (public static member function)
is_always_exhaustive [static] | determines if this layout mapping is always exhaustive (public static member function)
is_always_strided [static] | determines if this layout mapping is always strided (public static member function)
stride | obtains the stride along the specified dimension (public member function)

### Non-member functions

operator== | compares this layout mapping of `layout_left` with other mapping (function template)
submdspan_mapping(std::layout_left::mapping) (C++26) | calculates the mapping and data handle offset used for `subdmspan` (public member function)

### See also

mapping | a layout mapping of layout_right (public member class template of `std::layout_right`)
mapping | a layout mapping of layout_stride (public member class template of `std::layout_stride`)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/container/mdspan/layout_left/mapping&oldid=178734"